The invention relates to improvements in fuel-fired heat pump systems incorporating a heat store for utilizing rejected heat from the fuel-fired prime mover.
U.S. Pat. No. 4,976,464 incorporated herein by reference discloses an arrangement for improving the efficiency of a heat pump system by using the heat rejected by a fuel-fired prime mover in the space conditioning and potable water heating load at the occupied space of a building site. In particular, the system disclosed in the patent recognizes the benefits of using a conventional domestic hot water tank as a heat storage unit for the heat pump fuel-fired prime mover and teaches the avoidance of thermal cycling losses in the heat pump by periodically using heat in the tank to supply the heating load between periods of operation of the heat pump.
In a typical installation, the heat pump compressor and fuel-fired prime mover, usually an internal combustion engine (hereinafter engine), are situated in a cabinet outside of the building to reduce noise and simplify safety measures. Consequently, the compressor and engine are exposed to environmental temperature extremes. When the environmental air is cold, engine starting reliability can suffer and proper lubrication of both the engine and compressor during and following cold start up is difficult. Still further, cold starts of the engine can reduce energy efficiency and involve poor combustion so as to increase harmful engine exhaust emissions. Recognition of lubrication problems with electric heat pump compressors has lead to prior attempts to situate a heat pump compressor or air conditioning compressor indoors where temperature extremes are avoided.